The invention relates to a method of producing negative molds with microstructured recesses for forming in said recesses, by electrodeposition, plate-like microstructured bodies.
Several procedures for making such negative molds are described in U.S. Pat. No. 4,661,212.
In one of the procedures described in this patent, a mold release agent is applied to the front face portions of a microstructured master mold which is then coated with a layer of an electrically conductive polymethylmetacrylate (PMMA)/carbon black mixture. The pretreated master mold is then pressed into a layer of a casting resin whereby the PMMA/carbon black mixture becomes firmly attached to the casting resin so that, after removal of the master mold, the layer of casting resin becomes a negative mold for the microstructure and carries in its recesses the electrically conductive PMMA/carbon black coat.
A disadvantage of this process is that only negative molds with relatively coarse microstructures can be generated in this manner.
In accordance with another procedure described in U.S. Pat. No. 4,661,212 a layer of an electrically insulating thermoplastic casting resin is disposed on top of a layer of an electrically conductive material layer. The master mold is then pressed into the casting resin layer until the front face areas of the microstructures contact the electrically conductive layer such that, after removal of the master mold, the electrically conductive layer is exposed at the bottom of the structure recesses of the negative mold.
This procedure however requires the thermoplastic casting resin layer to be of accurate and constant thickness. It is furthermore difficult to control impression of the master mold to a degree that all its front face areas are pressed into contact with the electrically conductive layer.
In another procedure disclosed in U.S. Pat. No. 4,661,212 an electrically insulating casting resin is applied to the master mold and the casting resin material on top of the microstructures on the mold is then scraped off with a wiper-type structure so that only the recessed areas of the microstructure remain filled with casting resin. After partial curing of the thermoplastic resin an electrically conductive layer of a PMMA-carbon black mixture is applied. After curing and removal from the mold, the so-provided negative mold has the electrically conductive material exposed at the bottom of the microstructure recesses thereof.
A disadvantage of this procedure is that two different material layers must be applied to the master mold and first partial and then full curing of the layers must be awaited.
The molding of microstructured bodies is extensively discussed by H. Vollmer, W. Ehrfeld and P. Hagmann in a publication entitled "Fabrication of Microstructures with Extreme Structural Heights by Vacuum Reaction Injection Molding and Electroforming", Kernforschungszentrum Karlsruhe, KfK 4267 (May 1987).
In this report a vacuum molding process is described wherein insulating microstructures of PMMA are molded on top of a metallic base plate in a reaction injection molding process. The metallic base plate must be supplied, that is, manufactured, separately and must be provided for each mold recess with a molding bore.
During the molding procedure the base plate is disposed on the master mold. The mold recesses are then evacuated by way of the molding bores and subsequently filled with a reaction resin material. The reaction resin is cured in the mold recesses and defines negative microstructures which, after hardening of the resin, are firmly attached to the base plate. The master mold is removed and the microstructure is released from the master mold by side-guided separating movement of the master mold and the base plate. During the following electroforming procedure the base plate serves as collector electrode.
This process however is relatively involved because of the large number of molding bores required.
It is the principal object of the present invention to provide a method of producing molds for platelike microstructures which avoids the disadvantages of the known methods. Removal of the master mold should be achievable in a single step. The method should make it further possible to produce negative molds with microstructure recess bases coated with various electrically conductive materials in a simple and efficient manner.